/// <summary>
/// Update an entry in the list with data from an alarm
/// </summary>
/// <param name="i">Index in the list to update</param>
/// <param name="alarm">Alarm with the new data to display</param>
private void UpdateCollectionItem(int i, ObservableAlarmLine alarm)
{
// Local ID and message are assumed not to change
if (_alarmObserverCollection[i].Priority != alarm.Priority)
{
_alarmObserverCollection[i].Priority = alarm.Priority;
}
if (_alarmObserverCollection[i].State != alarm.State)
{
_alarmObserverCollection[i].State = alarm.State;
}
}
/// <summary>
/// Display a smoothly scrolling list of the 10 newest alarms
/// </summary>
public void onAlarmsReceivedMethod()
{
try
{
// If you know that your alarms are all new, you may clear the observable list and fill in from scratch, but that may cause flickering.
// The algorithm here is to avoid such flickering. It is a mini version of the code from the Smart Client plug-in.
int bottomIndex = _alarms.Length - 1;
for (int i = 0; i <= bottomIndex; i++)
{
// We assume that the alarms received are always ordered by time descending, and the Alarm.ID is unique per instance of an Alarm
// Thus is is given that if a given ID is ordered after another ID once, it will always be after that other ID.
//
// There are two possibilities
// A: The received item is new and does not appear in the collection,
// in which case we just add it to the top of the collection, but after those new ones already added
// B: The received item appears at this or a later position in the old collection
// in which case the old ones from the current position to the match position must have disappeared
// All those items are removed and the matching item is updated
ObservableAlarmLine alarm = new ObservableAlarmLine(_alarms[i]);
int match = FindId(i, alarm.AlarmLine.Id);
if (match == -1)
{
// The alarm is inserted as a new item, because it did not appear in the former collection
_alarmObserverCollection.Insert(i, alarm);
}
else
{
// If the match was some positions ahead, we are sure that those alarms skipped shall no longer be displayed
// Remember not to advance the index passed to RemoveAt(). When we have deleted position i, the old i+1 is not at the same position.
for (int j = i; j < match; j++)
{
_alarmObserverCollection.RemoveAt(i);
}
// We must then update the individual properties of the alarm in the list with those property values from the new alarm
// Just setting _alarmObserverCollection[i] = alarm cause the WPF list view's multiple selection mechanism to get confused.
UpdateCollectionItem(i, alarm);
}
}
// If the number of alarms received is less than in the original collection, we are left with a tail of alarms, which we don't know the actual status of
// Most likely, they will exist unaltered, but they may have had their data changed or they might have been deleted. We do not know that for sure.
// This implementation therefore removes them, which may cause selected items to disappear from the list view
// The exception is an empty list caused by a temporary connect error, where we want to keep all the old data
// If the list really it to be cleared, _eraseAlarmListBeforeUpdate should have been set to true
if (bottomIndex > 0)
{
int n = _alarmObserverCollection.Count - 1;
while (n > bottomIndex)
{
_alarmObserverCollection.RemoveAt(n);
n--;
}
}
}
catch (Exception)
{
// Go on. This is just for safety.
}
}